Each tube in this comparison was installed in the same custom-built, fixed-bias single-ended guitar amplifier in order to obtain the voltage gain measurements and conduct listening tests. Each tube sample used for comparison was chosen because it measured in the middle range of idle plate current draw at the same operating point set by a Maxi-Matcher Digital Tube Tester:
|Ia||=||24mA ("mid-range" DC plate current value measured in Maxi-Matcher)|
|Va||=||400 VDC (Maxi-Matcher's given plate voltage)|
|Vg1||=||-48 VDC (Maxi-Matcher's given control grid voltage)|
An audio frequency generator was used to sweep from 10Hz to 20kHz with the input voltage measured at the 6L6GC control grid (g1) and the output voltage measured at the output transformer's secondary winding while connect to an 8 ohm load. The 50Hz measurement was used for Lows, 700Hz for mids and 6kHz for highs.
A Comparison of Current Production 6L6GC Tubes
Also included in this comparison are direct substitutes for the 6L6GC including: KT66 and 5881.
The beam power part tells us that the tube, as RCA put it, "is a tetrode or pentode in which directed electron beams are used to increase substantially the power-handling capability of the tube. A feature of a beam power tube is its low screen-grid current. Because of the effective suppressor action provided by space charge and because of the low current drawn by the screen grid, the beam power tube has the advantages of high power output, high power sensitivity, and high efficiency." The 6L6GC is a type of beam power tube employing a beam-confining electrode at cathode potential in place of an actual suppressor grid.